This invention relates to an engine control device, and an engine control method which calculates a fuel injection quantity and ignition timing from a pressure in a combustion chamber at the time of acceleration or deceleration, to control the fuel injection quantity and the ignition timing.
FIG. 5 is a diagram showing the arrangement of a conventional engine control device disclosed by Unexamined Japanese Patent Application No. 253543/1989. In FIG. 5, reference numeral 61 designates an engine body. In the cylinder head 61a of the engine body 61, a sensor 62 for detecting a pressure in a cylinder (hereinafter referred to as "a cylinder pressure sensor 62", when applicable) and a sensor 63 for detecting a temperature in a Cylinder (hereinafter referred to as "a cylinder temperature sensor 63", when applicable) are provided for each of the cylinders. The cylinder pressure sensor 62 and the cylinder temperature sensor 63 have detecting parts which are exposed in the combustion chamber of the cylinder.
Injectors 64 are provided in suction ports 61b communicated the cylinders of the engine body 61. The suction ports 61b are communicated through a suction manifold 65 having a throttle chamber 66.
The upstream portion of the throttle chamber 66 is communicated through a suction pipe 67 to an air cleaner 68.
A timing sensor (or crank angle sensor) 610 for detecting crank angles preset for the cylinders is coupled to a distributor 691 which is coupled to a cam shaft (not shown).
On the other hand, an air/fuel ratio sensor 611 is provided at the junction of branch pipes of an exhaust manifold 69 which is communicated with exhaust ports 61c of the engine body 61. Further in FIG. 5 , reference numeral 612 designates a catalytic converter; and 613, a throttle valve.
Further in FIG. 5, reference numeral 614 designates a control unit (hereinafter referred to merely as "an ECU", when applicable) which is made up of a micro-computer including a CPU, RAM, ROM, input interface, etc. The input side of the ECU 614 is connected to the above-described cylinder pressure sensors 61, cylinder temperature sensors 63, timing sensor 610, and air/fuel ratio sensor 611.
The output side of the ECU 614 is connected through a drive circuit 615 to the injectors 64. Further in FIG. 5, reference numeral 615 designates ignition plugs, which are held by the cylinder head 61a. The output side of the ECU 614 is further connected through a drive circuit 617 to the ignition plugs 615.
The operation of the conventional engine control device thus organized will be described. The ECU 614 calculates a suction air quantity G.sub.a of each of the cylinders, for instance, according to the following Equation (1): EQU G.sub.a =(P.times.V)/(R.times.T) (1)
where P is the pressure in each cylinder (hereinafter referred to as "a cylinder pressure", when applicable) which the ECU 614 measures in synchronization with a crank angle (for instance BTDC 90.degree.CA (hereinafter a crank angle will be referred to as ".degree.CA", when applicable)) predetermined for the cylinder which crank angle is detected by the timing sensor 610, V is the volume of the combustion chamber at the predetermined crank angle, R is the gas constant in the stroke of compression, and T is the temperature of the gas in the cylinder which is measured with the cylinder temperature sensor (hereinafter referred to as "a cylinder temperature", when applicable).
On the other hand, Japanese Patent Application No. 221433/1984 has revealed the following fact: It is assumed that the cylinder pressure provided at bottom dead center (BDC) on the compression stroke differs by .DELTA.P from the cylinder pressure at 40.degree.CA before top dead center (TDC) as shown in FIG. 6. In this case, there is established a linear relationship between the quantity of air G.sub.a charged into the engine and the cylinder pressure difference .DELTA.P as shown in FIG. 7. Thus, the suction air quantity can be calculated from the difference .DELTA.P between cylinder pressures provided at two crank angles on the compression stroke.
On the other hand, Unexamined Japanese Patent Application No. 47836/1985 has disclosed the following method: Fuel injection times are obtained from a two-dimensional map of fuel injection times which is stored in the ROM of the ECU with the cylinder pressure differences .DELTA.P and engine speeds N as parameters.
The quantity of air G.sub.a charged in the engine is calculated by the ECU 614. By using the quantity of air G.sub.a thus calculated, a fuel injection pulse width T.sub.1 is calculated according to the following Equation (2): EQU T.sub.i =K.times.G.sub.a .times.K.sub.FB .times.K.sub.e ( 2)
where K is the air/fuel ratio constant; K.sub.FB is the air/fuel ratio feedback correction data; and K.sub.e is the correcting coefficient used for correcting the fuel injection pulse width according to the outputs of the cylinder temperature sensor and a cooling water temperature sensor. In response to the fuel injection pulse width thus calculated, the ECU 614 supplies a drive signal to the drive circuit 616, to drive the injectors 64 thereby to control the air/fuel ratio.
On the other hand, Unexamined Japanese Patent Application No. 103965/1984 has disclosed the following technique: The absolute value of a cylinder pressure as shown in FIG. 7 is measured at 40.degree.CA after bottom dead center, and the ECU 614 determines ignition timing referring to a predetermined two-dimensional map of ignition timing for each operating condition which is determined from cylinder pressures and engine speeds, and applies a drive signal to the drive circuit 617, to drive the ignition coils thereby to control the ignition timing.
Unexamined Japanese Patent Application No. 142228/1989 has proposed an engine control device which operates as follows: A suction air quantity is detected from a cylinder pressure or the rate of change of the cylinder pressure in the first half of the suction stroke, and the fuel injection is carried out in the second half of the suction stroke according to the suction air quantity thus detected.
The conventional engine control device is designed as described above. That is, the cylinder pressure value detected on a compression stroke is utilized. For this purpose, the quantity of air sucked into the cylinder is detected, and an air quantity detecting operation is delayed as much. Thus, when the engine is in transient state, the control of the air/fuel ratio and the ignition timing is lowered in accuracy. This is an essential problem to be solved for the device.
The conventional engine control device in which a suction air quantity is detected from a cylinder pressure or the rate of change of the cylinder pressure in the first half of the suction stroke suffers essentially from the following problems: When noises or the gain of the cylinder pressure sensor changes, a cylinder pressure P at a predetermined crank angle, or the cylinder pressure value detected on the suction stroke is affected by spitting or blow-by depending on pulse timing, and is lowered in accuracy because of the limitation in dynamic range of the cylinder pressure sensor. Thus, although the delay in detection of an air quantity is short, when the engine is in steady state the detection of a quantity of air charged in the engine is lowered in accuracy, with the result that the control of the air/fuel ratio and the ignition timing is lowered in accuracy.